This invention relates to an ink jet recording element. More particularly, this invention relates to an ink jet recording element containing pigments.
In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An ink jet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-forming layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support.
While a wide variety of different types of image-recording elements for use with ink jet devices have been proposed heretofore, there are many unsolved problems in the art and many deficiencies in the known products which have limited their commercial usefulness.
It is well known that in order to achieve and maintain photographic-quality images on such an image-recording element, an ink jet recording element must:
Be readily wetted so there is no puddling, i.e., coalescence of adjacent ink dots, which leads to non-uniform density
Exhibit no image bleeding
Exhibit the ability to absorb high concentrations of ink and dry quickly to avoid elements blocking together when stacked against subsequent prints or other surfaces
Exhibit no discontinuities or defects due to interactions between the support and/or layer(s), such as cracking, repellencies, comb lines and the like
Not allow unabsorbed dyes to aggregate at the free surface causing dye crystallization, which results in bloom or bronzing effects in the imaged areas
Have an optimized image fastness to avoid fade from contact with water or radiation by daylight, tungsten light, or fluorescent light
An ink jet recording element that simultaneously provides an almost instantaneous ink dry time and good image quality is desirable. However, given the wide range of ink compositions and ink volumes that a recording element needs to accommodate, these requirements of ink jet recording media are difficult to achieve simultaneously.
Ink jet recording elements are known that employ porous or non-porous single layer or multilayer coatings that act as suitable image receiving layers on one or both sides of a porous or non-porous support. Recording elements that use non-porous coatings typically have good image quality but exhibit poor ink dry time. Recording elements that use porous coatings typically have poorer image quality but exhibit superior dry times.
The above-referred to U.S. application Ser. No.09/451,786 by Sadasivan et al. relates to a porous ink jet recording element comprising a substrate having thereon an image-receiving layer comprising an inorganic, anionic pigment, an organic, anionic binder and an organic, cationic mordant. While that ink jet recording element provides good image quality and fast ink dry times, it would be desirable to improve the image quality, as measured by optical density.
U.S. Pat. No. 5,104,730 relates to an ink jet recording sheet comprising a substrate and porous ink absorbent layers formed upon the substrate, wherein the bottom layer is pseudo-boehmite and a binder and the top layer is a fine silica powder. However, there is a problem with this element in that the top layer has to be peeled-off after printing which reduces the image optical density.
It is an object of this invention to provide an ink jet recording element that has a fast ink dry time. It is another object of this invention to provide an ink jet recording element that has good image quality. It is another object of the invention to provide an ink jet recording element that has improved gloss.
These and other objects are achieved in accordance with the invention which comprises an ink jet recording element comprising a substrate having thereon an image-receiving layer comprising an inorganic, anionic pigment, an organic, anionic binder and an organic, cationic mordant, and a porous overcoat layer located over the image-receiving layer, the porous overcoat layer comprising an inorganic pigment and an organic, anionic, binder, wherein the refractive index of the inorganic pigment in the overcoat layer is at least 0.05 refractive index units less than the refractive index of the inorganic, anionic pigment in the image-receiving layer.
The ink jet recording element of the invention provides good image quality, fast ink dry times and improved gloss.
The inorganic, anionic pigment in the image-receiving layer useful in the invention may be a kaolin clay, a calcined clay, calcium carbonate, titanium dioxide, talc or a silicate. In a preferred embodiment of the invention, the inorganic, anionic pigment used is a kaolin clay sold under the trade name Hydragloss(copyright) 92 (J. M.Huber Company). The amount of inorganic, anionic pigment used may range from about 50% to about 95% of the image-receiving layer.
The organic, anionic binder of either layer useful in the invention may be a styrene acrylic latex; a styrene butadiene latex, such as Styronal(copyright) BN 4606X (BASF Corp.); a poly(vinyl alcohol); a poly(vinyl acetate), such as Vinac(copyright) 884 (Air Products Inc.); a cellulosic or a polyurethane binder. In a preferred embodiment of the invention, a commercially-available styrene acrylic latex such as Acronal(copyright) S-728 (BASF Corp.) is used in the image-receiving layer. In another preferred embodiment of the invention, a commercially-available poly(vinyl alcohol) such as Airvol(copyright) 21-205 (Air Products Inc.) is used in the overcoat layer.
The organic, anionic binder may be used in an amount of from about 5% to about 20% of the image-receiving layer or overcoat layer. In general, good results are obtained when the ratio of pigment to binder is from about 5:1 to about 8:1.
The organic, cationic mordant useful in the invention may be a polymer latex dispersion or a water-soluble polymer solution. Examples of mordants useful in the invention are disclosed in U.S. Pat. No. 5,474,843, the disclosure of which is hereby incorporated by reference. Other useful mordants include cationic urethane dispersions sold under the trade name Witcobond(copyright) W-213 and Witcobond(copyright)W-215 (Witco Corporation).
In a preferred embodiment of the invention, the organic, cationic mordant is:
M1: poly(N-vinyl benzyl-N-benzyl-N,N-dimethyl ammonium chloride-co-styrene-co-divinyl benzene),
M2: poly(N-vinylbenzyl-N,N,N-trimethylammonium chloride-co-ethylene glycol dimethacrylate), or
M3: poly(N-vinylbenzyl-N,N,N-trimethylammonium chloride-co-divinyl benzene).
In general, good results have been obtained when the mordant polymer is present in an amount of from about 1% to about 75% by weight of the image-receiving layer, preferably from about 10% to about 20%.
Smaller quantities of up to about 10 % of other binders may also be added to the image-receiving layer such as poly(vinyl pyrrolidone) sold as Luviskol(copyright)VA 64W (BASF Corp.) or poly(vinyl pyrrolidone-co-vinyl acetate) sold as Luviquat(copyright) PQ11PN (BASF Corp.). In addition to the above major components, other additives such as pH-modifiers like nitric acid, cross-linkers, rheology modifiers, surfactants, UV-absorbers, biocides, lubricants, dyes, optical brighteners etc. may be added as needed.
As noted above, the refractive index of the inorganic pigment in the overcoat layer is at least 0.05, preferably between about 0.15 and 0.25, refractive index units less than the refractive index of the inorganic, anionic pigment in the image-receiving layer. This overcoat layer is generally optically clear and causes a reduction in light scattering by the recording element. A reduction in light scattering results in superior optical density and gloss.
The inorganic pigment useful in the overcoat layer of the invention may be, for example, a silica (such as colloidal silica, fumed silica or silica gel), an alumina (an alumina oxide, an alumina hydrate or a pseudoboehmite), a calcium carbonate, a modified kaolin clay, a montmorillinite clay, a hydrotalcite clay or a laponite clay. In a preferred embodiment of the invention, the inorganic pigment is an alumina hydrate sold under the trade name Dispal(copyright) 23N4-80 (Condea Vista Company).
The amount of inorganic pigment used may range from about 50% to about 95% of the image-receiving layer.
The substrate may be porous such as paper or non-porous such as cellulose acetate or polyester films. The surface of the substrate may be treated in order to improve the adhesion of the image-receiving layer to the support. For example, the surface may be corona discharge treated prior to applying the image-receiving layer to the support. Alternatively, an under-coating or subbing layer, such as a layer formed from a halogenated phenol or a partially hydrolyzed vinyl chloride-vinyl acetate copolymer, can be applied to the surface of the support.
The ink jet coating may be applied to one or both substrate surfaces through conventional pre-metered or post-metered coating methods such as blade, air knife, rod, roll coating, etc. The choice of coating process would be determined from the economics of the operation and in turn, would determine the formulation specifications such as coating solids, coating viscosity, and coating speed. In a preferred embodiment, the image-receiving layer coating formulation would have a coating solids of 40-60% and a low shear (100 rpm Brookfield) viscosity of 500-2000 centiPoise. In another preferred embodiment, the overcoat layer coating formulation would have a coating solids of 20-40% and a low shear (100 rpm Brookfield) viscosity of 400-2000 centipoise.
The image-receiving layer thickness may range from about 5 to about 60 xcexcm, preferably from about 10 to about 30 xcexcm. The overcoat layer thickness may range from about 2 to about 20 xcexcm, preferably from about 4 to about 10 xcexcMm. The coating thickness required is determined through the need for the coating to act as a sump for absorption of ink solvent and the need to hold the ink near the coating surface.
After coating, the ink jet recording element may be subject to calendering or supercalendering to enhance surface smoothness. In a preferred embodiment of the invention, the ink jet recording element is subject to hot, soft-nip calendering at a temperature of about 65xc2x0 C. and pressure of 14000 kg/m at a speed of from about 0.15 m/s to about 0.3 m/s.
The substrate used in the ink jet recording element of the invention may be opaque, translucent, or transparent. There may be used, for example, plain papers, resin-coated papers, various plastics including a polyester resin such as poly(ethylene terephthalate), poly(ethylene naphthalate) and poly(ester diacetate), a polycarbonate resin, a fluorine resin such as poly(tetra-fluoro ethylene), metal foil, various glass materials, and the like. The thickness of the substrate employed in the invention can be from about 12 to about 500 xcexcm, preferably from about 75 to about 300 xcexcm.
Ink jet inks used to image the recording elements of the present invention are well-known in the art. The ink compositions used in ink jet printing typically are liquid compositions comprising a solvent or carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives, and the like. The solvent or carrier liquid can be solely water or can be water mixed with other water-miscible solvents such as polyhydric alcohols. Inks in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid may also be used. Particularly useful are mixed solvents of water and polyhydric alcohols. The dyes used in such compositions are typically water-soluble direct or acid type dyes. Such liquid compositions have been described extensively in the prior art including, for example, U.S. Pat. Nos. 4,381,946; 4,239,543 and 4,781,758, the disclosures of which are hereby incorporated by reference.
Although the recording elements disclosed herein have been referred to primarily as being useful for ink jet printers, they also can be used as recording media for pen plotter assemblies. Pen plotters operate by writing directly on the surface of a recording medium using a pen consisting of a bundle of capillary tubes in contact with an ink reservoir.
The following example further illustrates the invention.